Caster assemblies are well known. They are provided on a wide variety of articles that are moveable by rolling, including chairs and other furniture (tables, sofas, beds, etc.), stands for medical equipment and other instrumentation, cabinets, work surfaces, dollies, and the like. FIG. 1 shows one type of conventional caster assembly 10. Here, the caster assembly 10 includes a wheel 12 that is rotationally coupled to a caster frame 14. The caster frame 14 is coupled to a caster stem 16, which allows the caster assembly 10 to be attached to an article (not shown in FIG. 1) such that the wheel 12 is free to pivot relative to the article.
FIG. 2 shows an exploded view of a prior art caster assembly 200 that has no central hub. Such caster assemblies are known as hubless casters. Hubless casters typically provide a more aesthetically pleasing appearance, as compared to conventional hubbed casters. However, due to various design limitations, previous hubless casters have not delivered the performance necessary for widespread adoption.
One key performance deficiency of prior art hubless casters is durability. Certain prior art designs would simply wear out too quickly. One reason for this lack of durability relates to how the frame member 202 of such hubless casters 200 interfaces with the rolling element 204. The rolling element 204 shown in FIG. 2, for example, is mounted directly on a mount portion 206 of the frame member 202. In other words, the mount portion of the frame member itself defines the inner bearing race. As a consequence, when the caster rolls, rollers 208 (or ball bearings) of the rolling element 204 bear directly against the mount portion 206. Over time, this can cause the mount portion 206 to wear prematurely (note that in a design of this nature, the inner race defined by the mount portion is a primary wear component). As a result, the longevity and overall performance of the hubless caster can be diminished significantly.
Certain other prior art hubless casters lack durability, or do not perform as well as they could, due to a narrow distribution of load across the width of the mount portion 206. The width of an exemplary mount portion 206 is shown as W in FIG. 2. Some prior art hubless casters concentrate the load exerted on the mount portion in a narrow region of the mount portion. For example, a row of relatively small ball bearings may be provided, and these ball bearings may only contact a small width of the mount portion. The resulting highly concentrated load can accelerate wear on the mount portion, and this can impair the longevity and overall performance of such hubless casters.